Detrital subsidies lead to elevated densities of spiders and carabids in cucurbit crops by increasing abundances of detritivores, which are alternative prey for these generalist predators. In principle, such enhanced densities of spiders and carabids might not result in increased control of insect pests if the predators were to switch their feeding preferences to the detritus-based food chain. We used stable isotope analysis to investigate whether or not adding detritus to replicated 8x8-m cucurbit gardens changes the feeding relationships and trophic levels of spiders and carabid predators. In both control and detrital-subsidy gardens, small sheet-web spiders (Linyphiidae) and juvenile wolf spiders (Lycosidae) had d13C values similar to those of Collembola, suggesting that these detritivores may be a significant source of prey for these spiders in both types of gardens. In both treatments, adults of the largest wolf spiders (Lycosidae) and the predaceous ground beetles (Carabidae) had d13C values similar to those of herbivorous insect pests, suggesting that herbivores make up a significant source of prey for these generalist predators even in the presence of abundant detritivorous prey. Furthermore, trophic levels (estimated from d15N values) of carabids and large lycosids did not differ between detrital-subsidy and control gardens. These results suggest that adding detrital subsidies in order to enhance densities of generalist predators will not interfere with their overall effectiveness as biocontrol agents.
Species 1: Araneae Linyphiidae
Species 2: Araneae Lycosidae
Species 3: Coleoptera Carabidae
Keywords: stable isotopes, generalist predator
Back to Ten-Minute Papers, Section Ca. Biological Control
Back to Ten-Minute Papers, Section Ca, Cb, Cc, Cd, Ce, and Cf
Back to The 2003 ESA Annual Meeting and Exhibition